And the reason for that is that basically you needed a wire connecting from one phone to another: https://en.wikipedia.org/wiki/Circuit_switching
On the way to modern day digital packet switching (where you just send the bits for millions of connections down massive capacity pipes) there was multiplexing, etc. but it was a long and hard road.
Everything in NYC at the time was cash-only and metered. No refills on drinks. Ketchup packs were are a quarter each. I never saw so many hands out except for India. The people were much nicer in India, in NYC it was more your classic Klingon style “Buy something or die!”
I know this on a personal level.
I had a crazy friend in college who thought BHT (the preservative) could cure AIDS.
His phone bill was $350-500/month. He would call researchers around the country, even Dr. Fauci. (Fauci actually listened to him once, until he found out he didn't have any credentials.) He once called France to speak with a researcher at work, over Rock Hudson's treatment. The small business owner came in steaming. He said, "Who called France. The call cost me $500.00!"
Everyone was complaining about long distance charges.
It literally seemed like in was a few months after the breakup, and long distance calls were dirt cheap.
(It might have been longer than months, but it felt that way. It was then I realized the important antitrust laws, and how monopolies need to be slapped down.)
The heavy ISPs went to the government literally crying that it will break their business and they will lay off thousand of people.
They were sent away, wiped their tears and changed the price of a mobile contract from 80 to 10€.
They are still there and the customer is happy
You don't even have to go all the way back to the 70s or 80s to see this. We used to pay by the minute for dial up internet and cell phone calls well into the 00s.
The "all you can eat" business model — whether ad-supported or for a fixed monthly fee — is a very recent invention, and is only possible because of massive improvements to the underlying infrastructure (fiber, LTE, cheap servers).